The present invention relates to an image forming apparatus such as a digital copying machine wherein an image on an original is scanned by a scanner and printed out on paper by a printer.
In conventional digital copying machines, there are the following methods of detecting sheet sizes of paper sheets to be fed from sheet cassettes at the time of image formation:
(1) The user chooses one of sizes displayed on an operation panel of a digital copying machine.
(2) A sheet size detection mechanism is provided in a sheet cassette. In an example of the detection mechanism, the positions of side guides and end guides, which are made to match with a paper sheet, are detected stepwise.
In the case of (1), although the cost is low because the detection mechanism is not provided, it is inconvenient that the user has to input the sheet size.
In the case of (2), the machine body cost is high because the detection mechanism is required. Moreover, only fixed sizes can automatically be detected. The number of automatically detectable sizes is limited. When the size varies on the order of mm, as in the case of non-fixed sizes, input or setting is required.
Specifically, in either of the cases (1) and (2), when a paper sheet is of a non-fixed size, there is a problem that the user has to input or set the sheet size on the operation panel.
The object of the present invention is to provide an image forming apparatus capable of detecting and setting a sheet size, without increasing a machine body cost or imposing a load on a user.
This invention may provide an image forming apparatus having a plurality of cassettes for containing paper sheets, and forming an image on a paper sheet fed from one of the cassettes, the apparatus comprising: a designating section which designates the cassette in which a paper sheet for image formation by the image forming apparatus is to be set; an image read section which reads an image of the paper sheet to be set in the cassette designated by the designating section, when the paper sheet is placed on an original table; and a control section which executes a control to detect the size of the paper sheet on the basis of the image read by the image read section.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.